The present disclosure relates generally to circuit breakers and particularly to cassette type molded case circuit breakers.
While conventional molded case circuit breakers may utilize a base that is a solid structural part of the breaker and acts to bear the loads of pressure and magnetic repulsion forces during a short circuit event, cassette-type circuit breakers can utilize a breaker base that is a protective shell rather than an actual structural part of the circuit breaker. Cassette breakers disposed within the base are designed to be the load-bearing members during a short circuit event, rather than the breaker base. In an example of a 3-phase circuit breaker, the cassettes are 3 individual poles and the pressure and magnetic forces on the breaker during a short circuit event create repulsive forces between the cassettes. If left unsupported, the cassettes would then spread apart and exert a significant undesirable stress on side walls of the base of the circuit breaker.
Methods to prevent such undesirable stress include increasing a thickness of side walls of the base, increasing venting, and reducing stress concentrations in the base. Additional solutions include use of hardware such as a rivet or screw, for example to secure the cassettes to each other, and thereby prevent them from spreading apart and applying force to the side walls of the base. Although these methods may be effective, increasing side wall thickness, within defined external envelope dimensions, results in a reduction of internal volume available for active circuit protection components, to which a rated current capacity is typically directly related. Further, use of hardware to secure cassettes together has the disadvantage of typically including a metal rod to span a width of all the cassettes within the breaker, thereby potentially creating a reduction in phase-to-phase dielectric isolation.
Accordingly, there is a need in the art for a circuit breaker arrangement that overcomes these drawbacks.